While Malebranche thought there was no intersubstance interaction, German philosopher Gottfried Wilhelm Leibniz (1646-1716) attempted to take a further step. For Leibniz, reality doesn’t consist of two kinds of substances—mind and body— because, for Leibniz, substances are indivisible and body (in the Cartesian sense) is divisible. Hence, body cannot be a substance, only mind can. Reality consists of an infinite number of mind substances, which he terms “monads.” The universe unfolds in terms of these monads according to God’s pre-established harmony. Monads don’t interact to realize or cause the unfolding. Whatever happens in the universe is a result of God’s perfect coordination among them. God’s universe is a preprogrammed universe consisting of these monads.1
According to idealist bishop George Berkeley (1685-1753), we suppose matter exists, yet we never experience it directly. We supposedly experience mediated mental events between us and the material world. In his view, it is impossible to directly encounter matter. Moreover, we cannot exit our minds to see how our perceptions correspond to reality. Why then claim that there is a material world? According to Berkeley, only minds and mental contents exist. How could this be? Suppose I leave my cell phone at home and go shopping; how can the cell phone exist without anyone thinking about it? What about distant galaxies, solar systems, and black holes that no minds have encountered; how could they exist without anyone contemplating them? Berkeley, like Descartes, relies on God. God thinks of everything, including mobile phones in drawers and distant galaxies. God sustains reality through conscious awareness.